Cable-television (CATV) systems are widely used in the transmission of programs to receiving stations at shielded or isolated locations where normal viewing by antenna-fed receivers is unsatisfactory. In such systems the programs are relayed to various distribution points by separate high-frequency cables which may be part of a common trunk line. In a branched distribution system the receiving stations are connected to such a trunk line at various junctions; in a radial array a number of receiving stations are served through a common distribution center at the end of a trunk line.
In conventional CATV systems of the latter type, the subscribers at the receiving stations may select their programs with the aid of a switching network at the common distribution center, the switches of that network responding to d-c or low-frequency signals transmitted to the network over a line separate from the one used for supplying the selected program to the subscriber station.